"I used Lewis Black (as Anger) from the very beginning pitch, while other characters came later," he says.

"The actors contributed heavily to the writing, sometimes literally. In the case of Bill and Amy we said 'write with them'. Other times it just happened at the microphone, listening to the way they speak."

Inside Out's opening was highly anticipated not only because it was Pixar's first film in two years, but also because it received an eight-minute standing ovation at Cannes.

"Just having people respond and laugh is great," he says.

"I think it's really universal. Everyone around the world has the same emotions and reacts to things in a similar way.

"There is a lot of pressure in the world and we do spend a lot of time asking ourselves 'How can I be happier?'. But there's a reason why we have all of these emotions in there. Life is complex, full of disappointment and loss as well as happiness."